The present invention relates to a circuit for and a method of controlling brushless DC motors, particularly 4-phase DC motors.
The rotating fields required to convert electrical energy into mechanical energy by means of electric motors can be produced mechanically (brushes making contact with collectors of a rotor) or electronically with the aid of semiconductor switches. U.S. Pat. No. 4,484,115 discloses a brushless DC motor having a stator which is provided with 7 phase windings and is connected in star or in a ring circuit. The rotor of the DC motor is covered with permanent magnets. The current required to produce a rotating field is controlled with the aid of semiconductor switches which are driven by signals from a rotor position sensor. Each phase winding has two semiconductor switches associated with it to permit bipolar operation.
From German Patent 33 01 801, it is known to operate a star-connected 4-phase brushless DC motor in a bipolar mode with only four semiconductor switches instead of eight semiconductor switches.
The aforementioned brushless DC motor described in the U.S. patent has the disadvantage of requiring one pair of complementary transistors for each phase winding. This is a complicated and costly solution. The brushless DC motor disclosed in German Patent 33 01 801 has the disadvantage that the stator windings are connected in star, so that the stator cannot be fully wound automatically. In addition, soldering is necessary on the coil winding heads, and the latter become relatively large in the axial direction, which results in additional electric losses.